BioMedical Admissions Test (BMAT) Practice Test 2026 - Free BMAT Practice Questions and Study Guide

Antidiuretic hormone (ADH), also known as vasopressin, is primarily responsible for regulating water retention in the kidneys. When the body is dehydrated or when blood osmolarity increases, ADH is released from the posterior pituitary gland. It acts on the kidney's nephrons, specifically the collecting ducts, increasing their permeability to water. As a result, more water is reabsorbed back into the bloodstream rather than excreted in urine. This function is crucial in maintaining osmoregulation and overall fluid balance in the body.

While other options, such as glycogen storage, muscle mass increase, and blood glucose levels, are important physiological processes, they are regulated by different hormones and mechanisms. For example, glycogen storage is largely affected by insulin and glucagon, muscle mass is influenced by growth hormone and testosterone, and blood glucose levels are primarily influenced by insulin. Therefore, ADH’s specific role in water retention distinctly sets it apart, affirming that the primary regulation attributed to ADH is indeed water retention in the kidneys.